Iterated in vitro reproduction and genetic orphans
In an article soon to be published in the Journal of Medical Ethics, Rob Sparrow imagines a procedure via which multiple generations of human embryos might be created in the laboratory. Egg and sperm cells would first be generated from existing or new human pluripotent stem cell lines. The resulting eggs would be fertilised using the sperm to create zygotes and ultimately embryos. Embryonic stem cells would then be harvested from these embryos and used to create new egg and sperm cells, which would in turn be used to fertilise one another to create further embryos. This process could be iterated, in principle indefinitely.
Let’s call this procedure ‘iterated in vitro reproduction’ (Sparrow calls it ‘in vitro eugenics’). Iterated in vitro reproduction is not yet possible, but, citing recent developments in the science of stem cell-derived gametes, Sparrow argues that it may well become so, though he acknowledges are number of significant hurdles to its development. He also discusses a number of possible applications of the technology and calls for an ethical debate on these. The most controversial application would be in the creation of designer children. Consider the following case, which is a variant on one of the scenarios imagined by Sparrow:
Jack and Jill present to a fertility clinic. Jack provides a sperm sample, and fertility doctors harvest a number of eggs from Jill. These eggs are fertilized with Jack’s sperm to create embryos, from which embryonic stem cells are derived. These stem cells are then induced to develop into eggs or sperm which are used to fertilise one another, and so on. The process is iterated numerous times, and at each stage, the embryos are genetically screened via pre-implantation genetic diagnosis. This screening is used to inform a process of selective crossing, so that, over several generations, the population of embryos evolves towards certain genetic dispositions desired by Jack and Jill (a disposition towards longevity, say). This process is aided by adding small amounts of genetic material from stem cell lines derived from other individuals. Eventually, doctors identify an embryo with almost exactly the desired combination of genes, and this embryo is implanted into Jill’s womb and carried to term. A child, Jarvis, is born.
Cases like this raise numerous ethical issues, some of which are discussed by Sparrow and the seven commentators on his paper. However, they also raise an interesting conceptual question: would the users of such a technology be the genetic parents of the resulting offspring? Would Jack and Jill be the genetic parents of Jarvis?
Sparrows argues not. Though he does not himself discuss a case in which the resulting child’s genetic material comes predominantly from the couple who employ the technology, as in the case of Jack and Jill, it is clear what he would say about this case: even if Jarvis inherited approximately 50% of his DNA from each of Jack and Jill, Jack and Jill would not be his genetic parents. Given the intervening generations of embryos, Jack and Jill could at most be Jarvis’ genetic great-great-….grandparents (though they would of course also be his social parents). Jarvis would, in Sparrow’s terms, be a ‘genetic orphan’: an individual with no living genetic parents. (On this, see also an earlier paper by Sparrow.)
Interestingly, although a number of the commentators on Sparrow’s paper discuss the ethical implications of the claim that children like Jarvis would be genetic orphans, none question the claim itself. Yet I think there might be scope to question it. I think it could be argued that Jarvis is the genetic child of Jack and Jill.
What makes one individual the genetic parent of another? A initial, rough-and-ready definition might hold that P is the genetic parent of C if and only if
(a) C inherited some (or perhaps some specified proportion) of his or her genetic material from an egg or sperm derived from P, and
(b) the genetic material was not transmitted from the former to the latter via another individual.
The first condition serves to rule out cases in which the latter is not the genetic descendant of the former. The second serves to rule out cases in which the latter is the genetic descendent of the former, but not a direct descendant; the relation is one of genetic grandparenthood or some more indirect genetic relation, not one of genetic parenthood. (Obviously the notions of ‘inheritance’ and ‘transmission via’ would need to be further spelled out.)
Condition (a) is too restrictive, however. There are other species that reproduce asexually, without the creation of eggs or sperm, yet I would be inclined to say that there can still be genetic parenthood relations between the members of such species. Moreover, if it were possible for humans to reproduce without the creation of eggs and sperm, but in ways that nevertheless involved combining 50% of the genetic material from each member of a couple to produce an embryo, we would, I think, still be inclined to call the members of that couple the genetic parents of the child. This suggests that we need to drop the reference to eggs and sperm in condition (a) and allow for other forms of genetic inheritance.
Condition (b) also requires modification. In every normal process of human reproduction, the parents pass genetic material to the resulting child via another ‘individual’ being, though not an individual human being: rather, they transmit genetic material via an individual eggs or sperm. Yet this would not lead us to conclude that, in normal reproduction, the reproducing individuals are really the genetic grandparents of the resulting child and it is the sperm or egg that is the parent. This suggests that we need to specify what kind of individual the intermediate descendant would need to be in order to break the genetic parenthood link. Plausibly, it would need to be a human being.
If we adopt the modifications suggested by these thoughts, then we might end up with something like the following account. P is the genetic parent of C if and only if
(a*) C inherited some (or perhaps some specified proportion) of its genetic material from P, and
(b*) the genetic material was not transmitted from the former to the latter via another human being.
Note, however, that on this definition, Jack and Jill may well qualify as the genetic parents of Jarvis. This is because it is not obvious that the intervening generations produced in the course of iterated in vitro reproduction that lead to Jarvis’ creation are generations of human beings. Some deny that zygotes and early human embryos qualify as human beings on the grounds that they lack the required intercellular integration. The embryo becomes a human being only when its component cells become integrated with and dependent on one another. Before then, the embryo is better thought of as simply a colony of human stem cells. On this view, early embryos are rather like gametes: they are not human beings themselves, they are rather intermediaries formed in the creation of one human being from others.
One attractive feature of this view can be seen by considering the case of monozygotic twins. Suppose Chris and Carol have monozygotic twins, Diana and Dahlia. Monozygotic twins are created by the splitting of one zygote (that is, a fertilized egg) or early embryo into two. That zygote/embryo goes out of existence when it splits to create the twins. Thus, it seems plausible to say that Chris and Carol transmit their genetic material to Diana and Dahlia via a zygote/embryo that is distinct from the two post-splitting zygotes from which they developed. Yet we would not want to say that this intermediary zygote was Diana and Dahlia’s genetic parent and Chris and Carol are the genetic grandparents. Rather, we would say that Chris and Carol are the genetic parents of the twins. The view that zygotes and early embryos are not human beings and the account of genetic parenthood that I offered above are together able to accommodate this: they allow us to maintain that the Chris and Carol are the genetic parents of the twins since the intervening individual is not a human being.
Likewise, if we accept these views, there is a case for concluding that iterated in vitro reproduction needn’t break ties of genetic parenthood. There is a case for concluding that Jack and Jill are the genetic parents of Jarvis, for Jarvis arguably inherited a proportion (perhaps almost 50%) of his genetic material from Jack and Jill, and the intervening generations of embryos were not generations of human beings.